Wireless Mesh Networks 4 WMNs consist of two types of nodes: mesh routers: forwarding data. mesh clients: acting as hosts; forwarding data. The architecture of WMNs can be classified into three main groups: Backbone Client WMNs Hybrid WMNs
Client WMNs 6 One type of radio on devices Supporting end-user applications
Hybrid WMNs 7
Characteristics 8 Multi-hop wireless networking Extend the coverage range Provide non-line-of-sight connections Ad hoc networking Self-forming, self-healing, self-organization Low upfront investment costs Quick deployment
Characteristics (2) 9 Enabling integration of various existing networks (WiFi, WiMax, Internet, cellular, sensor networks) through gateway/bridge functionalities in mesh routers. Mobility: depending on the types of mesh nodes Power and resource constraints: mesh router: usually non restrictive mobile devices: limited power supply, storage, computing resources.
Applications 10 Broadband Home Networking Community Networking Enterprise Networking Metropolitan Area Networks Transportation Systems Building Automation Health and Medical Systems Security Surveillance Systems
Broadband Home Networking 11
Community Networking 12
Enterprise Networking 13
Metropolitan Area Networks 14
Transportation Systems 15
Many Other Applications 16 BACnet: Building Automation and Control NETworking
WMNs: Challenges 17 Wireless channels: error-prone media Low bandwidth channels Scalability Quality of service (QoS) guarantee Security Comparability, interoperability Mobility
Scalability 18 When the size of network increases, the network performance degrades significantly. Current IEEE MAC protocol and its derivatives cannot achieve a reasonable throughput as the number of hops increases to 4 or higher. For b, the TCP throughput is lower than 1 Mbps.
Single Channel: Capacity 19 Theoretical upper limit of the per node throughput capacity : Experimental results from CSMA/CA MAC on a string topology: throughput ≈ 1 / n
Scalability (2) 20 Routing protocols may not be able to find a reliable routing path. Transport protocols may loose connections. MAC protocols may experience significant throughput reduction.
Scalability (3) 21 CSMA/CA has very low frequency spatial-reuse efficiency. Centralized medium access schemes such as TDMA, CDMA are difficult to implement Ad hoc nature of WMNs Complexities of TDMA, CDMA Time synchronization of TDMA
Security 22 Routers, devices: physically vulnerable Jamming attacks No centralized trusted authority to distribute public keys in a WMN due to distributed system architectures.
Critical Design Factors 23 Scalability Security Compatibility and interoperability WiFi, WiMax, ZigBee, cellular, Internet Broadband and QoS end-to-end delay, delay jitter, PDR, throughput, fairness Mesh connectivity Self-organization, topology control Topology-aware MAC and routing
Critical Design Factors (2) 24 Ease of use As automatic as possible (power management, self-organization, topology control, fault tolerance, fast subscription/authentication) For quick and inexpensive deployment Radio techniques Directional and smart antennas MIMO systems Multi-radio/multi-channel systems Software radio
Mobile Ad hoc Networks (MANETs) 25 No infrastructure (no base stations or access points) Mobile nodes Form a network in an ad-hoc manner Act both as hosts and routers Communicate using single or multi-hop wireless links Topology, locations, connectivity, transmission quality are variable.
MANETs: Operations 26 S X Y D S X Z D
MANETs vs. WMNs 27 One type of radio on devices Supporting end-user applications
MANETs vs. WMNs (2) 28 MANETs: end-user devices also perform routing and configuration functionalities for all other nodes. WMNs: mesh routers perform these tasks. Mesh routers vs. mobile devices: power and resource constraints mobility MANETs: usually only one radio. WMNs: can have multiple channels, multiple radios.
MANETs: Applications 29 Civil Disaster recovery Taxi cabs Communications over water using floats Vehicular ad-hoc network Military Battlefield communications Monitoring and planning